Read This to Be Informed About the Barometer Units

Barometer Units
If you are looking for information on barometer units, you have landed on the right page. Here you will find a list of new as well as old units, along with a conversion table.
ScienceStruck Staff
Last Updated: Jun 3, 2018
"For those who want some proof that physicists are human, the proof is in the idiocy of all the different units which they use for measuring energy." - Richard Feynman (The Character of Physical Law)
As Professor Feynman said, even the various barometer units used by meteorologists all over the world are proof that meteorologists are human and are responsible for contributing their share of confusion to the world. Barometers are widely used instruments in meteorology to measure the pressure exerted by Earth's atmosphere. If you think that the Fahrenheit-Celsius-Kelvin conversion is confusing, wait till you read about the barometric units for atmospheric pressure measurement, that are detailed in this Buzzle article.
Barometers come in two main types which include mercury barometers and aneroid barometers. Their principle of operation varies but they are both actuated by changes in the surrounding atmospheric pressure. In mercury barometers, the rise of mercury is taken to be a measure of atmospheric pressure, while an aneroid barometer uses the contraction of evacuated cells to measure pressure. Calibration of the instruments according to units, is an important part of their design.
Barometer Units of Measurement
There needs to be a universal and clearly defined set of units for various physical quantities involved in scientific observations and inquiry. Without them, communication between people of science around the world would be difficult. Same is the case with units for air pressure measurement. Here are the units used for barometer based pressure measurements, along with a conversion table.
Conversion Table
Units Torr psi
1 Torr = 1 mm Hg 19.337 x 10-3 psi
1 psi 51.715 Torr = 1 lbf/inch2
1 Millibar 750.06 x 10-3 Torr 14.5037744 x 10-3 psi
1 Pascal 7.5006 x 10-3 Torr 145.04 x 10-6 psi

Conversion Table
Units Millibar Pascal
1 Torr 1.332 millibar 133.322 Pa
1 psi 68.948 millibar 6.895 x 103 Pa
1 Millibar = 103 dyne/cm2 100 Pa
1 Pascal 10-2 millibar = 1 Newton/m2

Millimeters of Mercury (Hg) / Torr
The first barometer was created by Evangelista Torricelli in 1643, using an evacuated inverted tube placed in a container of mercury. The pressure exerted by the overlying layers of the atmosphere make mercury rise into the tube. Thus the millimeter rise in the mercury level inside the tube was considered to be a measure of atmospheric pressure previously. The barometer unit of '1 mm Hg' is approximately equal to '1 Torr' of pressure. Thus 'mm of Hg' and 'Torr' are two interchangeably used units. One Torr equals to 133.322 Pascal or 19.337 x 10-3 pound force per square inch (psi).
Pascal (Pa)
The SI unit of pressure is Pascal which is defined to be one newton per meter square. It is the internationally used barometer unit. One Pascal is equal to 7.5006 x 10-3 Torr or 145.04 x 10-6 pound force per square inch (psi). One standard atmospheric pressure, abbreviated as 'atm', is equal to 101,325 Pascal. A commonly used subunit is hectopascal which is equal to 100 Pascal. In fact, hectopascal is the unit adopted by the International Meteorological Society to measure atmospheric pressure. Normal atmospheric pressure equals to 762.1 mm of Hg or 1016 hectopascals.
Pounds Force Per Square Inch (PSI)
Another barometer unit is 'Pounds Force Per Square Inch (psi)'. One psi equals to 6894.757 Pascal or 51.715 Torr. Also known as pound per square inch, 1 psi is the resultant of one pound-force exerted on an area extending for one square inch.
Millibar (mbar / mb)
Millibar is another widely used unit in barometer measurement. One bar is equal to 100 kilopascal, which is roughly equal to normal atmospheric pressure measured at sea level on Earth. Atmospheric pressure variation is usually measured in millibars, which is one thousandth of a bar and equal to 100 Pascal.

Barometric pressure readings can be in any of the above units but the most common ones are Torr and millibar. If you need to use these units frequently, just make a chart of these units, along with their interconversion formulas. Place it in front of you, near your work desk, where you can easily see it everyday. You will automatically memorize the units that way.